Re: Tagger energy resolution? (fwd from David)

[Elton Smith <elton@jlab.org>]

Hi Richard,

I am confused about point #3: How do we get an rms of 3 MeV including the
electron beam energy spread? From #1 that would be 60 MeV, but if you use
the 0.1% from other beam requirements, that is 12 MeV (sigma). Perhaps
"the intrinsic tagger resolution" is only refering to the uncertainty in
the energy of the the scattered electron e', but not the uncertainty in
the energy of the photon ephoton = ebeam - e'?

Thanks, Elton.

On Thu, 21 May 2009, Richard Jones wrote:

> Eugene,
>
> Ok, I think I misunderstood your meaning.  You are saying that the full energy bite
> of the microscope corresponds to +/- 2 sigma of the typical final state energy
> resolution in GlueX.  That tells me that the tracking+calo resolution is just good
> enough to say whether or not the beam photon was somewhere in the microscope, but
> not good enough to narrow it down much further within that range.  That appears to
> be true, although there will probably be some accidentals reduction coming from a
> chi-square cut on energy conservation.  I guess I was focused on trying to help
> clear up the questions raised by David about how the different numbers for the
> tagger energy resolution fit together into a coherent story.  I hope that story is
> clearer for him at this point
>  1. GlueX physics requires < 60 MeV rms resolution in the tagger microscope for
>     reconstructing exclusive final states.
>  2. Segmentation for rate purposes requires individual counters subtend < 10 MeV
>     full width in the microscope.
>  3. Intrinsic tagger resolution limits from electron beam energy spread and magnetic
>     optics are around 3 MeV rms in the region of the microscope.
>  4. Choice of 2mm fibers leads to 8 MeV full-width energy channels, consistent with
>     the rate requirements and exploiting the full resolution of the magnet + beam
>     for a final instrumental RMS energy resolution around 5 MeV rms.
> Richard Jones